title: One amino Acid change in cucumber mosaic virus RNA polymerase determines virulent/avirulent phenotypes on cowpea.
abstract: ABSTRACT The elicitation of the hypersensitive response (HR) is known to depend on the interaction between a resistance gene of a host plant and a corresponding avirulence gene of a pathogen. The cv. Kurodane-Sanjaku of cowpea (Vigna unguiculata) has the Cry locus that confers resistance against cucumber mosaic virus strain Y (CMV-Y). The resistance is overcome by infection with a legume strain of CMV (CMV-L). RNA 2, which codes for the 2a protein, a subunit of the viral replicase components, has been known to control virulent/avirulent phenotypes. We generated chimeric constructs of full-length cDNA clones of RNA 2 of both strains and inoculated infectious transcripts to delimit the domain controlling symptoms. A 243-base pair fragment containing a coding region for the GDD RNA-dependent RNA polymerase core sequence was shown to be responsible for the phenotypic differences. From sequence alignment analysis, two amino acids (Phe631 and Ala641) of the HR-type 2a protein encoded in this fragment were specifically exchanged to Tyr and Ser, respectively, in the 2a proteins of resistance-breaking strains. Point mutations introduced into RNA 2 backgrounds of both strains that were designed to change the amino acid at position 631 resulted in a change of symptoms, indicating that a single nucleotide change determines the reactions elicited by both strains. Analysis for one additional mutant RNA 2 showed that symptom determination may be correlated with the nature of the lateral chain of amino acid 631.
authors.forename: A
authors.initials: A
authors.lastname: Karasawa
authors.forename: I
authors.initials: I
authors.lastname: Okada
authors.forename: K
authors.initials: K
authors.lastname: Akashi
authors.forename: Y
authors.initials: Y
authors.lastname: Chida
authors.forename: S
authors.initials: S
authors.lastname: Hase
authors.forename: Y
authors.initials: Y
authors.lastname: Nakazawa-Nasu
authors.forename: A
authors.initials: A
authors.lastname: Ito
authors.forename: Y
authors.initials: Y
authors.lastname: Ehara